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The Smallest of Nanotubes Yielding Big Results

by Pam Frost Gorder

As Yoke Khin Yap typed an email from Boston, the five-day nanotechnology symposium that he organized was only half over. But he already had news to report.

His research team had discovered a new way to make nanotubes out of silicon—the stuff of computer chips. Their method is unusual because it’s compatible with the normal manufacturing methods already used in the chip industry. That means that one day, manufacturers could use the new method to build nanometer-sized structures into chips easily and affordably. And that could be the key to making smaller, faster computers.

Though the tiny tubes (pictured on these pages) that Yap makes in his laboratory can be only a few atoms wide, they are super-strong. The secret: each tube, no matter how long, is really just one big molecule, held together by very powerful atomic bonds. One spindly tube may look fragile when you view it through an electron microscope, but if you could hold it in your hands, you couldn’t pull it apart.

That’s why Yap became excited about nanotechnology in the first place. “Imagine that one can synthesize carbon nanotubes simply by baking nanoparticles of metals such as iron, nickel, or cobalt, in the presence of alcohol or acetylene—welding gas! And they become hundreds of times stronger than steel, yet five times lighter,” he says.

Yap, associate professor of physics, was definitely in his element at the 2007 Materials Research Society Fall Meeting. His nanotube symposium was the largest of the meeting, and all forty-one other symposia concerned advanced materials and nanotechnology in some way. Scientists discussed how to build nanomaterials atom by atom, how to form them into particular shapes, and how to adapt them for applications as diverse as microelectronics and alternative energy.

Carbon has been scientists’ favorite building block for nanotechnology ever since this area of research boomed in the 1990s. It has the strong atomic bonds—and also the versatility—to suit many different applications. Arrange its atoms one way, and carbon conducts electricity; arrange them another way, and it acts as an insulator. Carbon nanotubes could one day be used as electrical wires or as containers for even smaller objects. Their potential is nearly endless.

But the big news from Yap’s symposium was that, like him, more researchers are starting to build nanotubes out of materials other than carbon. By utilizing other common industrial materials such as silicon, Yap and his colleagues are bridging the gap between nanotechnology research and industry.

“We are continuously making new nanotubes and finding ways to understand them,” he says.

For example, of all the materials at his disposal, silicon would be the best choice for nanotubes that could be integrated into a computer chip. But while many researchers have succeeded in making silicon nanowires (solid nanorods instead of the new silicon nanotubes discovered by Yap’s group), nobody has been able to “dope” them with extra atoms to boost their conductivity, as chipmakers normally dope silicon wafers.

Nobody could do it, that is, until now. Yap’s team has succeeded in making doped silicon nanotubes, a new semiconducting nanomaterial. They grow the nanotubes like tiny blades of grass on top of a doped silicon wafer.

That’s one of five presentations his team gave at the meeting, and Yap’s team wasn’t the only Michigan Tech representatives who were on hand and making an impact. Ravi Pandey, physics chair and professor, lectured on the potential of nanotubes made from boron. And Craig Friedrich, professor of mechanical engineering, made a presentation of his own, on a technique for depositing nanotubes on microcircuit electrodes.

Several Michigan Tech graduate students made presentations as well—a testament to the fact that they are getting hands-on nanotech experience in their education. An influx of government funding, including that from Yap’s National Science Foundation CAREER award, has helped make that happen. (Other Michigan Tech NSF CAREER winners are profiled on page 15.)

“The research awards that we have obtained in the last few years have created a team of young nanoscientists here and added new facilities as well,” Yap says. “These have become important resources for nanotech education at Michigan Tech.”

Undergraduate students are benefiting, too, by taking a new minor in nanoscale science and engineering and getting the chance to do real research in Michigan Tech labs. Some of Yap’s former undergraduate lab workers have gone on to do graduate work at prominent universities such as MIT, Illinois, and Cal-Irvine—institutions that, like Michigan Tech, are making nanotechnology a reality.